Quantitative Solvent-Free Thermal Synthesis of Luminescent Cu(I) Coordination Polymers

Abstract

The luminescent Cu­(I) coordination polymers [Cu2I2(m,m′-bpy)] n (CuI- m; m,m′-bpy = m,m′-bipyridine; m = 3, 4) were successfully synthesized by the solvent-free thermal reaction of the metal salt CuI with the organic linkers m,m′-bpy. Powder X-ray diffraction analysis revealed that CuI-3 was immediately formed when a mixture of CuI and 3,3′-bpy was ground in a mortar at room temperature (20 °C). In contrast, a temperature >120 °C was required to synthesize the CuI-4 isomer, probably because of the higher melting point of the 4,4′-bpy linker. Although excess bpy linker was necessary to afford the CuI- m in high yield, the quantitative synthesis, without any purification processes, was successfully achieved by simple heating at 140 °C, whereby the excess bpy linker was thermally removed by evaporation. Single crystal X-ray structural analysis indicated that in CuI-3 the dinuclear {Cu2I2} rhombic cores were bridged by 3,3′-bpy linkers. A similar structure was observed for CuI-4; however, the intermolecular π–π stacking that was effective in CuI-4 was suppressed in CuI-3 because of the twisted configuration of the two pyridyl rings of the 3,3′-bpy linker. CuI-3 exhibited bright green emission with the maximum (λem) at 519 nm and a high emission quantum yield (Φ = 0.58) in the solid state at room temperature, in contrast to the weak red emission of CuI-4 (λem = 653 nm, Φ < 0.01). Emission decay analysis and density functional theory calculations suggested that the CuI- m emissions could be attributed to the delayed fluorescence from the metal-to-ligand charge-transfer excited state effectively mixed with the halide-to-ligand charge-transfer excited state.

Pyridine-Conjugated Pillar[5]arene: From Molecular Crystals of Blue Luminescence to Red-Emissive Coordination Nanocrystals

“…Remarkably, the microsecond-scale lifetime can be essentially prolonged under lower temperature and reduced at higher temperature, as measured from 77 to 377 K (Figure d and e, Table S4). The long luminescence lifetime and temperature-dependent property of Cu­(I)-P5bipy in the solid state are characteristic of phosphorescent emission, which is in good agreement with the reported Cu­(I) coordination materials. , …”

“…The long luminescence lifetime and temperature-dependent property of Cu(I)-P5bipy in the solid state are characteristic of phosphorescent emission, which is in good agreement with the reported Cu(I) coordination materials. 29,30 Solvochromic properties of Cu(I)-P5bipy nanocrystals have also been investigated. Two different emission bands were observed when the nanocrystals were dispersed in ethanol, acetone, and toluene, locating in the wavelength ranges of 400−450 nm and 460−600 nm, respectively, while only one emission band at 450 nm emerged in the dispersion of DMSO (Figure S16a).…”

Syntheses, Crystal Structures and Photophysical Properties of Dinuclear Copper(I) Complexes Bearing Diphenylphosphino‐Substituted Benzimidazole Ligands

“…The emission decay time of 1 drastically increases from τ obs =5.64 μs at 310 K to 59.05 μs at 10 K. Moreover, the relationship of lifetime and temperature exhibits a sigmoidal profile. These phenomena are similar to the cases which the TADF mechanism is applied, suggesting that the emission could be assigned to TADF from 1 (M+X)LCT at ambient temperature [9b] . According to the literature, the observed lifetime data can be expressed as a function of the temperature as shown in eq1. [25] …”

Copper(I) complexes with remotely functionalized phosphine ligands: Synthesis, structural variety, photophysics and effect onto the optical properties

“…Though a few scattered reports describing the photophysics of dinuclear {Cu2X2L4} species, where L is a N-and/or P-ligand, were reported previously [28][29][30][31], the first extensive investigation was carried out by Sasaki, Tsuge and co-workers on compounds of the family [Cu(µ-X)(PPh3)L]2 and [Cu(µ-X)L2]2 with different ligand combinations (L = is pyridine/substituted pyridine or a saturated amine) [12,32,33] that highlighted the effect of the halogen and p-accepting ability of the N-containing ligand on the nature of the emitting excited state. Following works by Kato and coworkers investigated the photoluminescence properties of the [Cu(µ-X)L2]2 scaffold bearing P-and S-ligands, [34][35][36] as well as of coordination polymers containing the dinuclear {Cu2X2} scaffold [37,38]. In addition, Bräse described a novel family of highly luminescent either homo-or heteroleptic complexes consisting of a butterfly-shaped {Cu2X2} skeleton and bearing various heteroaromatic P^N bridging ligands [15,39,40].…”